When various parts are to be soldered to a printed board, or IC is to be soldered to an IC socket, it is common to preliminarily treat the printed board with a flux in order to improve the adhesion of the solder. Usually, a flux contains an acidic component and thus is corrosive. Accordingly, it is necessary to prevent adhesion or penetration of a flux at an electric contact portion of an electronic part such as a connector, a switch, a volume or a pre-set resistor or at a portion where no soldering is required in a printed board. Especially in a case of an electronic part, soldering is frequently carried out at a through-hole portion. A phenomenon such that a flux creeps such a through-hole portion by e.g. a capillary phenomenon and penetrates or deposits at an unnecessary portion of the electronic part, is called "creeping of a flux", and it is necessary to prevent such a phenomenon.
For the purpose of preventing penetration or deposition of the flux, an agent for preventing creeping of a flux is used. As agents for preventing creeping of a flux for soldering, the following examples are known.
(1) A composition containing a compound having a polyfluoroalkyl group or a polymer thereof, as an essential component (JP-A-60-49859). Such a composition contains, as a solvent, a hydrocarbon type solvent such as heptane, an ester type solvent such as ethyl acetate, a chlorofluorocarbon (CFC) such as 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113), or a perfluorocarbon (PFC) having a boiling point of from 60 to 120.degree. C., or a fluorine-containing aromatic hydrocarbon type solvent such as 1,3-bis(trifluoromethyl)benzene.
(2) A composition having a low molecular compound containing polyfluoroalkyl groups or a polymer containing polyfluoroalkyl groups, dissolved in an alcohol solvent such as ethanol.
(3) A composition having a fluorine polymer obtained by polymerizing tetrafluoroethylene, a perfluoro (alkylvinyl ether) or vinylidene fluoride, a surfactant and an extender, dispersed in water (JP-A-5-175642.
(4) An aqueous dispersion comprising a copolymer of C.sub.8 F.sub.17 SO.sub.2 N(CH.sub.2 CH.sub.2)CH.sub.2 CH.sub.2 OCOCH.dbd.CH.sub.2 with dodecyl methacrylate, and an emulsifier containing no fluorine (JP-A-62-149784).
However, conventional agents for preventing creeping of a flux for soldering, have the following problems.
The composition (1) requires a due care, since the organic solvent is inflammable, and further, it has a problem from the viewpoint of the working environment, since it contains a volatile solvent. Further, when the solvent is a hydrocarbon type solvent, there will be problem that the solubility of the fluorine-containing component in the composition is poor. Further, with respect to CFC among the solvents, its influence over the ozone layer is feared, and its use is restricted by regulations relating to fluorocarbons. HCFC-225 or HCFC-141b, as a substitute for CFC, has similar problems. Further, PFC has a high coefficient for warming up the earth, and its influence over the environment is feared. The fluorine-containing aromatic hydrocarbon type solvent is inflammable and has a problem of odor.
The composition (2) is required to have the fluorine content of the low molecular weight compound or the polymer lowered in order to increase the solubility of such a compound or a polymer in the alcohol solvent. Further, the effect for preventing creeping of a flux is inadequate.
The fluorine polymer in the composition (3) is non-adhesive and poor in wettability and adhesion to the surface of an electronic part as a substrate. Accordingly, it is practically required to add a spreader. Further, this fluorine polymer has a softening point higher than 150.degree. C., and heat treatment at a high temperature is required in order to form a film by drying the fluorine polymer particles deposited on a substrate by means of a spreader. The temperature for this heat treatment will be higher than the heat resistant temperatures of most of parts having plastic portions, and practically, there is a problem that such heat treatment can not be done. On the other hand, if no heat treatment is applied, white solid fluorine polymer particles are likely to deposit as white solid on electronic parts, and there will be a drawback that the gloss of the treated surface is impaired.
The composition (4) has a problem that the surface tension is high and its wettability to the surface of electronic parts as substrates, is poor, and when it is practically coated on an electronic part, coating irregularities are likely to result. Further, when such a composition is deposited on an electric contact portion, there is a problem that electric conduction tends to be poor.